This invention relates to a baseband signal processor for used in a base station of a CDMA communication system, particularly, relates to a baseband signal processor capable of dealing with multirate and multiuser communication.
A well known mobile communication system includes base stations and mobile terminals. Each of the base stations covers a cell and communicates with the mobile terminals located in the cell.
With recent rapid increase of the number of the mobile terminals (or subscribers), usable frequency resources for the mobile communication system are rapidly decreasing. A CDMA (Code Division Multiple Access) communication system is therefore noted because it is higher than all other known communication systems in the frequency utilization efficiency.
By the way, data communication, such as visual data transmission, enjoys an increasing demand in field of mobile communication. The CDMA communication system must therefore deal with not only multiuser communication but also multirate communication from call of a low transmission rate to visual data transmission of a high transmission rate.
A conventional baseband signal processor (or RAKE receiver) is provided in the base station of the CDMA communication system. The baseband signal processor has a plurality of panels to process an input signal which includes a plurality of diffused signals. The number of the panels is equal to the maximum number of mobile terminals that can communicate with the base station through message channels. Each of the panels is formed so as to be possible to process the input signal at the maximum transmission rate for the CDMA communication system and forms a block which is the minimum unit for processing the diffused signals transmitted from one of the mobile terminals.
This type of the RAKE receiver is also used in the mobile terminal. Such RAKE receivers are disclosed in Unexamined Japanese Patent Publication No. Tokkaihei 10-94041, No. Tokkaihei 10-98448, and No. Tokkaihei 10-117157.
As mentioned above, all of the panels can deal with the maximum transmission rate. This is surfeit of equipment provided in the base station as a matter of fact. That is, the conventional baseband signal processor is larger than it needs in size and is expensive.
On the other hand, it is desirable that a cell covered by the base station is smaller, because necessary output power of the base station may be smaller and the frequency resources can be more efficiently used. However, it is necessary to increase the number of base stations in a service area of the CDMA communication system if cells become small. This brings an increase of investment in plant and equipment and an increase of the cost of maintenance for the CDMA system. These expenses are shifted onto the subscribers.
It is therefore an object of this invention to provide a baseband signal processor capable of dealing with multirate and multiuser communication with smaller structure than it needs.
Other object of this invention will become clear as the description proceeds.
On describing the gist of this invention, it is possible to understand that a baseband signal processor is used in a base station of a CDMA communication system. The baseband signal processor processes an input signal including a plurality of first diffused signals. The first diffused signals are originated from a first original diffused signal which is transmitted from a first mobile terminal at a first transmission rate.
According to the gist of this invention, the baseband signal processor comprises a plurality of processing panels to abstract specific data sequences from the input signal. A RAKE section is connected to the processing panels and is synthesize the abstracted data sequences to produce the synthesized data sequence. A controller is related to the processing panels and connected to the RAKE section. The controller selects at least one of the processing panels in response to the first transmission rate to abstract the first derivative data sequences as the specific data sequences and to produce first abstracted data sequences as the abstracted data sequences. The controller make the RAKE section produce a first synthesized data sequence as the synthesized data sequence.
According to another gist of this invention, the input signal includes a plurality of second derivative data sequences originated from a second original data sequence included in a second transmission signal transmitted from a second mobile terminal at a second transmission rate. The controller selects other one or more of the processing panels in response to the second transmission rate to abstract the second derivative data sequences as the specific data sequences and to produce second abstracted data sequences as the abstracted data sequences. The controller making the RAKE section produce a second synthesized data sequence which is time-divisionally multiplexed with the first synthesized data sequence.